JP7645173B2 - Printing device, printing system, and printing method - Google Patents

Description

This invention relates to a technology for printing by ejecting ink from an ejection head, and in particular to a technology for recovering ink supplied from a supply tank to an ejection head in a recovery tank, while sending ink from the recovery tank to the supply tank using a circulation pump, thereby circulating ink to the ejection head.

The printing device described in Patent Document 1 includes a supply tank and a recovery tank, each connected to the ejection head, and sends ink from the supply tank to the recovery tank via the ejection head by making the pressure in the recovery tank lower than the pressure in the supply tank. In addition, the printing device includes a circulation pump that sends ink from the recovery tank to the supply tank. This creates an ink circulation path that returns the ink that has reached the recovery tank from the supply tank via the ejection head to the supply tank.

The printing device also includes a solenoid valve between the recovery tank and the supply tank. This solenoid valve isolates the recovery tank from the supply tank when power is applied, but connects the recovery tank to the supply tank when power is not applied. With this configuration, if the circulation pump stops due to a power outage or the like, the pressure difference between the recovery tank and the supply tank is eliminated, and the flow of ink from the supply tank to the recovery tank can be stopped. This makes it possible to prevent ink from overflowing from the recovery tank.

JP 2020-44823 A

However, in the above printing device, the negative pressure in the recovery tank increases as the recovery tank and the supply tank communicate with each other. This can cause the negative pressure in the recovery tank to be insufficient relative to the head pressure between the recovery tank and the ejection head, resulting in ink leaking from the ejection head.

This invention was developed in consideration of the above problems, and aims to provide a technology that makes it possible to prevent ink leakage from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated.

The printing device according to the present invention includes an ejection head that ejects ink from a nozzle, a recovery tank that stores ink recovered from the ejection head, a buffer unit that communicates with the recovery tank, a supply tank that stores ink to be supplied to the ejection head, a first pressure applying unit that applies a first pressure to the supply tank, a second pressure applying unit that applies a second pressure, which is a negative pressure lower than the first pressure, to the recovery tank and the buffer unit, a circulation pump that uses supplied power to perform a liquid transfer operation to transfer ink from the recovery tank to the supply tank, and a circulation pump that is provided between the supply tank and the recovery tank and that, when power is applied, causes the supply tank to The device is equipped with a bypass solenoid valve that isolates the ink tank from the recovery tank and the supply tank when the supply tank is not energized, and a power supply unit that supplies power to the circulation pump and the bypass solenoid valve, the recovery tank being disposed above the ejection head, and the buffer unit that communicates with the recovery tank and the supply tank when the bypass solenoid valve is not energized generates a third pressure in the recovery tank and the supply tank, which is a negative pressure higher than the second pressure and lower than the first pressure, and the third pressure resists the head pressure between the recovery tank and the supply tank and the nozzle of the ejection head to prevent ink from leaking from the nozzle.

The printing method according to the present invention includes the steps of: applying a first pressure to a supply tank connected to a discharge head that discharges ink from a nozzle to perform printing, while applying a second pressure, which is a negative pressure lower than the first pressure, to a recovery tank connected to the discharge head and to a buffer unit communicating with the recovery tank, thereby supplying ink from the supply tank to the discharge head and recovering ink from the discharge head to the recovery tank; supplying power to a circulation pump provided between the recovery tank and the supply tank to send ink from the recovery tank to the supply tank; and, when the supply of power to the circulation pump is stopped, communicating the recovery tank and the supply tank with each other, communicating the buffer unit with the recovery tank and the supply tank, generating a third pressure, which is a negative pressure higher than the second pressure and lower than the first pressure, in the recovery tank and the supply tank, and the third pressure resists the head pressure between the recovery tank and the supply tank and the nozzle of the discharge head to prevent ink from leaking from the nozzle.

In the present invention (printing device and printing method) configured in this way, a buffer section is provided that communicates with the recovery tank. Then, when the recovery tank and the supply tank are mutually blocked, a first pressure is applied to the supply tank, and a second pressure, which is a negative pressure lower than the first pressure, is applied to the recovery tank and the buffer section. In this configuration, when the supply tank and the recovery tank are connected to each other, the difference between the first pressure in the supply tank and the second pressure in the recovery tank and the buffer section is eliminated, and the pressure in the recovery tank increases. However, since the buffer section is provided separately from the recovery tank, the increase in pressure in the recovery tank is suppressed compared to when there is no buffer section. Specifically, a third pressure, which is a negative pressure higher than the second pressure and lower than the first pressure, is generated in the recovery tank and the supply tank, and this third pressure prevents ink leakage from the nozzle against the head pressure between the recovery tank and the supply tank and the nozzle of the ejection head. This makes it possible to prevent ink from leaking from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated.

The printing device may also be configured such that the first pressure applying unit has a first solenoid valve and a first pressure tank connected to the supply tank via the first solenoid valve, and applies the first pressure generated in the first pressure tank to the supply tank via the first solenoid valve, and the first solenoid valve communicates the supply tank and the first pressure tank when energized, while isolating the supply tank and the first pressure tank from each other when deenergized, and the second pressure applying unit has a second solenoid valve and a second pressure tank connected to the recovery tank via the second solenoid valve, and applies the second pressure generated in the second pressure tank to the recovery tank via the second solenoid valve, and the second solenoid valve communicates the recovery tank and the second pressure tank when energized, while isolating the recovery tank and the second pressure tank from each other when deenergized. In such a configuration, as the supply tank and the recovery tank are communicated, the first and second pressure tanks are isolated from the supply tank, the recovery tank, and the buffer unit. Therefore, the third pressure required to prevent ink leakage from the ejection head can be reliably generated in each of the supply tank, recovery tank, and buffer section.

The printing device may also be configured so that the first pressure is a positive pressure. In other words, in a configuration in which positive pressure is generated in the supply tank, the problem of ink leakage described above tends to become more pronounced. Therefore, it is particularly suitable to apply the present invention to such a configuration.

The printing device may also be configured so that the ink is white ink. That is, white ink is often used to print so-called solid images that form backgrounds, etc. When printing such solid images, if the amount of white ink ejected from the ejection head is insufficient, image defects such as streaks appearing in areas where the white ink does not adhere can occur. In response to this, applying positive pressure inside the supply tank allows a sufficient amount of white ink to be ejected from the ejection head, making it possible to print a suitable solid image.

The printing system according to the present invention includes the above-mentioned printing device and a drying device that dries the ink ejected onto a print medium by the printing device. In this printing system, too, it is possible to prevent ink from leaking from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated.

As described above, according to the present invention, it is possible to prevent ink leakage from the ejection head when the pressure difference between the supply tank that supplies ink to the ejection head and the recovery tank that recovers ink from the ejection head is eliminated.

FIG. 1 is a front view showing a schematic diagram of an example of a printing system according to an embodiment of the present invention. FIG. 2 is a front view showing a schematic diagram of a printing device included in the printing system shown in FIG. 1 . FIG. 2 is a diagram illustrating a schematic configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head. FIG. 2 is a diagram illustrating a schematic configuration of a discharge head and an ink supply mechanism that supplies ink to the discharge head.

Figure 1 is a front view showing a schematic example of a printing system according to the present invention. In Figure 1 and the following figures, the horizontal direction X and the vertical direction Z are appropriately indicated. As shown in Figure 1, the printing system 1 includes a printing device 3 and a drying device 6 arranged in the horizontal direction X. This printing system 1 transports a long strip-shaped printing medium M from a pay-out roll 11 to a take-up roll 12 in a roll-to-roll manner. The material of the printing medium M is a film such as OPP (oriented polypropylene) or PET (polyethylene terephthalate). However, the material of the printing medium M is not limited to a film, and may be paper or the like. Such a printing medium M is flexible. In the following, the surface on which an image is printed of both sides of the printing medium M will be appropriately referred to as the front surface M1, and the surface opposite the front surface M1 will be appropriately referred to as the back surface M2.

The printing device 3 prints an image on the surface M1 of the printing medium M by ejecting water-based ink by inkjet printing onto the surface M1 of the printing medium M transported from the pay-out roll 11 to the take-up roll 12. The detailed configuration of the printing device 3 will be described later. The printing medium M on which the image has been printed in this manner is transported in the horizontal direction X from the printing device 3 to the drying device 6.

The drying device 6 includes a drying oven 60, which dries the printing medium M discharged from the printing device 3 as it is transported from the pay-out roll 11 to the take-up roll 12. The drying oven 60 includes two upper blowing units 61u arranged in the horizontal direction X, two middle blowing units 61m arranged in the horizontal direction X below the upper blowing units 61u, and two lower blowing units 61l arranged in the horizontal direction X below the middle blowing units 61m.

The printing medium M discharged from the discharge port 312 of the printing device 3 passes through two upper blowing units 61u in the horizontal direction X, and is then folded back by a pair of rollers 62 toward two middle blowing units 61m. Next, the printing medium M passes through two middle blowing units 61m in the horizontal direction X, and is then folded back by a pair of air turn bars 63 toward two lower blowing units 61l. Furthermore, the printing medium M passes through two lower blowing units 61l in the horizontal direction X, and is then discharged outside the drying device 6.

The upper blowing unit 61u has two blowing chambers 64 arranged to sandwich the printing medium M passing in the horizontal direction X from the vertical direction Z. Each blowing chamber 64 has multiple nozzles 65 arranged in the horizontal direction X, and each nozzle 65 sprays hot air (gas at 60 degrees or higher) onto the printing medium M. In this way, the printing medium M is dried by the hot air sprayed from the nozzles 65 of these blowing chambers 64 as it passes between the two blowing chambers 64 arranged above and below. Similarly to the upper blowing unit 61u, each of the middle blowing unit 61m and the lower blowing unit 61l also has two blowing chambers 64 that sandwich the printing medium M from the vertical direction Z.

The specific configuration of the upper blower unit 61u is not limited to this example. For example, instead of the lower blower chamber 64 of the upper and lower blower chambers 64 of the upper blower unit 61u, multiple rollers arranged in the horizontal direction X may be provided. In this configuration, the back surface M2 of the printing medium M can be supported from below by the multiple rollers, while hot air can be sprayed from the upper blower chamber 64 onto the front surface M1 of the printing medium M.

Figure 2 is a front view showing a schematic of a printing device provided in the printing system of Figure 1. In Figure 2, one side X1 and the other side X2 of the horizontal direction X are appropriately shown. Here, one side X1 is the side facing the drying device 6 from the printing device 3, and the other side X2 is the opposite side to one side X1. The printing device 3 includes a housing 31, a color printing unit 32 arranged in the housing 31, a white printing unit 33 arranged above the color printing unit 32 within the housing 31, and a transport unit 4 that transports the printing medium M by a plurality of rollers arranged within the housing 31.

The color printing unit 32 has multiple (six) ejection heads 321 arranged in the direction of travel of the printing medium M (direction from the other side X2 to the one side X1) above the printing medium M transported by the transport unit 4. Each of the multiple ejection heads 321 has a nozzle that faces the surface M1 of the printing medium M that passes below it from above, and ejects color inks of different colors from the nozzles using an inkjet method. Here, color ink means ink other than white, and includes inks such as cyan, magenta, yellow, and black. In this way, each of the multiple ejection heads 321 of the color printing unit 32 prints a color image on the surface M1 of the printing medium M by ejecting color inks from above onto the surface M1 of the printing medium M that passes below it.

The white printing unit 33 also has a single ejection head 331 arranged above the printing medium M transported by the transport unit 4. The ejection head 331 has a nozzle that faces the surface M1 of the printing medium M that passes below it from above, and ejects white ink from the nozzle using an inkjet method. In this way, the ejection head 331 of the white printing unit 33 prints a white image on the surface M1 of the printing medium M by ejecting white ink from above onto the surface M1 of the printing medium M that passes below it.

An inlet 311 opens in the side wall of the other side X2 of the housing 31, while an outlet 312 opens in the side wall of the one side X1 of the housing 31. The transport unit 4 transports the print medium M from the inlet 311 to the outlet 312, passing through the color printing unit 32 and the white printing unit 33.

The transport unit 4 has an entrance unit 41 provided below the color printing unit 32, an upward transport unit 42 provided on one side X1 of the color printing unit 32, an upward transport unit 43 provided above the color printing unit 32, and a downward transport unit 44 provided on the other side X2 of the color printing unit 32. The entrance unit 41 transports the print medium M carried in from the entrance 311 to one side X1 by rollers 411, the upward transport unit 42 transports the print medium M carried by the entrance unit 41 to the upward side by rollers 421, the upward transport unit 43 transports the print medium M carried by the upward transport unit 42 to the other side X2 by rollers 431, and the downward transport unit 44 transports the print medium M carried by the upward transport unit 43 to the downward side by rollers 441.

The transport unit 4 further includes a color transport unit 45 that supports the printing medium M facing the color printing unit 32 from below, and the printing medium M that has passed through the downward transport unit 44 enters the color transport unit 45. This color transport unit 45 has multiple rollers 451 arranged from the other side X2 to one side X1, and each roller 451 contacts the back surface M2 of the printing medium M from below. Thus, the front surface M1 of the printing medium M supported by the color transport unit 45 faces upward, and each ejection head 321 of the color printing unit 32 ejects color ink while facing this front surface M1 from above.

The transport unit 4 also has rollers 461, 462, and 463 arranged between the color transport unit 45 and the downward transport unit 44 in the traveling direction of the print medium M. The roller 461 is a drive roller that drives the print medium M. The rollers 462 and 463 are driven rollers that rotate in response to the print medium M.

The transport unit 4 further includes a reversing transport unit 47 that turns upside down the print medium M transported from the color transport unit 45 to the one side X1 twice. The reversing transport unit 47 includes a plurality of rollers 471-477, including a drive roller 471, and turns upside down the print medium M twice while these rollers 471-477 contact the back surface M2 of the print medium M. In other words, the reversing transport unit 47 transports the print medium M transported from the color transport unit 45 downward by the rollers 471 and 472, and then changes the travel direction of the print medium M to the other side X2 by the roller 472 and transports it, thereby turning upside down the front surface M1 and the back surface M2 of the print medium M. Next, the reversing transport unit 47 transports the print medium M from the one side X1 to the other side X2 by the plurality of rollers 473, and then transports the print medium M upward by the rollers 474-476. Furthermore, the reverse transport unit 47 uses rollers 476 to change the direction of travel of the print medium M to one side X1, thereby again inverting the front surface M1 and back surface M2 of the print medium M, and uses rollers 477 to transport the print medium M from the other side X2 to one side X1.

The transport unit 4 also has a white transport unit 48 that supports the print medium M facing the white printing unit 33 from below, and the print medium M that has been inverted twice by the inversion transport unit 47 enters the white transport unit 48. This white transport unit 48 has a roller 481 that contacts the back surface M2 of the print medium M from below. Thus, the front surface M1 of the print medium M supported by the white transport unit 48 faces upward, and the ejection head 331 of the white printing unit 33 ejects white ink while facing this front surface M1 from above.

The transport unit 4 also has an unloading unit 49 that is provided above the upper transport unit 43. The unloading unit 49 has a number of rollers 491 arranged from the other side X2 to one side X1 in the horizontal direction X. This unloading unit 49 transports the print medium M transported by the white transport unit 48 to the one side X1 using the multiple rollers 491, thereby unloading the print medium M from the unloading opening 312 of the housing 31 to the drying device 6.

As described above, the color printing unit 32 and the white printing unit 33 of the printing device 3 have ejection heads 321, 331. Next, the ink supply mechanism that supplies ink to these ejection heads 321, 331 will be described. The basic configuration of the ink supply mechanism is common to the ejection heads 321, 331. Therefore, the explanation will focus on the ejection head 331 that ejects white ink. In addition, hereafter, the ejection heads 321, 331 will be referred to as ejection heads H as appropriate.

3 and 4 are schematic diagrams showing the configuration of an ejection head and an ink supply mechanism that supplies ink to the ejection head, with FIG. 3 showing the state during power transmission and FIG. 4 showing the state during a power outage. As shown in both figures, the ejection head H has a housing Ha, and a plurality of nozzles N are arranged and open at the bottom of the housing Ha. Inside the housing Ha, a plurality of cavities Hb each communicating with the plurality of nozzles N and an ink supply chamber Hc communicating with the plurality of cavities Hb are provided, and ink supplied from the ink supply chamber Hc is stored in the cavity Hb. Then, a piezoelectric element provided in the cavity Hb pushes ink out of the cavity Hb, and ink is ejected from the nozzle N communicating with the cavity Hb. Note that the specific method of ejecting ink does not depend on the method using a piezoelectric element, and may be a thermal method of heating the ink. Additionally, an ink inlet Hd and an ink outlet He are open at the top of the ejection head H, and ink flows from the ink supply mechanism 9 into the ink supply chamber Hc via the ink inlet Hd, and flows from the ink supply chamber Hc to the ink supply mechanism 9 via the ink outlet He.

The ink supply mechanism 9 includes a supply tank 91 connected to the ink inlet Hd via a pipe 911, and a recovery tank 92 connected to the ink outlet He via a pipe 922. Ink is stored in each of the supply tank 91 and the recovery tank 92. Each of the supply tank 91 and the recovery tank 92 is disposed above the ejection head H. The ink supply mechanism 9 includes a circulation pump 93 disposed in a pipe 932 that connects the flow path between the recovery tank 92 and the supply tank 91, which sends ink from the recovery tank 92 to the supply tank 91, and a degassing filter 931 disposed in the pipe 932 at a position between the circulation pump 93 and the supply tank 91. The degassing filter 931 removes gas from the ink before it flows out of the circulation pump 93 and into the supply tank 91.

The ink supply mechanism 9 has a power supply circuit 94 that supplies power to each component of the device. The circulation pump 93 sends ink from the recovery tank 92 to the supply tank 91 using the power supplied from the power supply circuit 94 (liquid sending operation). As a result, the circulation pump 93 performs an ink circulation operation that circulates ink through a circulation path C that travels from the recovery tank 92 through the supply tank 91 to the ink supply chamber Hc of the ejection head H and then back to the recovery tank 92.

The ink supply mechanism 9 also includes a main tank 951 capable of storing a large amount of ink, and a main pump 952 that is disposed in a pipe 953 that connects the main tank 951 and the recovery tank 92 through a flow path, and sends ink from the main tank 951 to the recovery tank 92. When the ink circulating through the circulation path C decreases due to the ejection of ink from the nozzles N, the main pump 952 uses power supplied from the power supply circuit 94 to replenish ink from the main tank 951 to the recovery tank 92.

The ink supply mechanism 9 further includes a supply-side pressure applying unit 96 (hereinafter, appropriately referred to as the "pressure applying unit 96") that applies a positive pressure P1 to the supply tank 91. The pressure applying unit 96 includes a pressure tank 961, a pump 962 that applies a positive pressure P1 inside the pressure tank 961 by supplying gas (air) to the pressure tank 961, and a flexible tube 963, one end of which is connected to the pressure tank 961. In the pressure applying unit 96, the pump 962 supplies gas to the pressure tank 961 using power supplied from the power supply circuit 94. The positive pressure P1 thus generated in the pressure tank 961 by the pump 962 is applied to the supply tank 91 via the tube 963 and further the piping 934.

In contrast, gas (air) accumulates above the ink surface in the supply tank 91. In other words, in the supply tank 91, ink is stored below the gas-liquid interface, and gas exists above the gas-liquid interface. Therefore, the pressure applying unit 96 applies a positive pressure P1 to the gas-liquid interface in the supply tank 91.

The pressure applying unit 96 also includes an electromagnetic valve 964 provided between the other end of the tube 963 and one end of the piping 934. This electromagnetic valve 964 is of a normally closed type. Therefore, during the power transmission shown in FIG. 3, the electromagnetic valve 964 creates a state of communication between the atmosphere of the pressure tank 961 and the supply tank 91 by the power supplied from the power supply circuit 94, and the positive pressure P1 inside the pressure tank 961 is applied to the inside of the supply tank 91 via the tube 963, the electromagnetic valve 964, and the piping 934. On the other hand, during the power outage shown in FIG. 4, the power supply from the power supply circuit 94 to the electromagnetic valve 964 is lost, so the electromagnetic valve 964 creates a state of blocking the atmosphere between the pressure tank 961 and the supply tank 91, and the application of the positive pressure P1 from the pressure tank 961 to the supply tank 91 is blocked.

The pressure applying unit 96 has a check filter 965 between the pipe 934 and the solenoid valve 964. This check filter 965 allows the passage of gas from the supply tank 91 to the pressure tank 961, while prohibiting the passage of ink from the supply tank 91 to the pressure tank 961. In this way, the check filter 965 prevents ink from flowing from the supply tank 91 into the tube 963.

The ink supply mechanism 9 also includes a recovery side pressure applying unit 97 (hereinafter, appropriately referred to as the "pressure applying unit 97") that applies negative pressure to the recovery tank 92. The pressure applying unit 97 includes a pressure tank 971, a pump 972 that reduces the pressure inside the pressure tank 971 by sucking gas (air) from the pressure tank 971, and a flexible tube 973, one end of which is connected to the pressure tank 971. In the pressure applying unit 97, the pump 972 exhausts gas from the pressure tank 971 using power supplied from the power supply circuit 94. The negative pressure P2 thus generated in the pressure tank 971 by the pump 972 is applied to the recovery tank 92 via the tube 973 and further the piping 944.

In contrast, gas (air) accumulates above the ink surface in the recovery tank 92. That is, in the recovery tank 92, ink is stored below the gas-liquid interface, and gas exists above the gas-liquid interface. Therefore, the pressure applying unit 97 applies a negative pressure P2 to the gas-liquid interface in the recovery tank 92.

The pressure applying unit 97 also includes an electromagnetic valve 974 provided between the other end of the tube 973 and one end of the piping 944. This electromagnetic valve 974 is of a normally closed type. Therefore, during the power transmission shown in FIG. 3, the electromagnetic valve 974 creates a state of communication between the atmospheres of the pressure tank 971 and the recovery tank 92 by the power supplied from the power supply circuit 94, and the negative pressure P2 inside the pressure tank 971 is applied to the inside of the recovery tank 92 via the tube 973, the electromagnetic valve 974, and the piping 944. On the other hand, during the power outage shown in FIG. 4, the power supply from the power supply circuit 94 to the electromagnetic valve 974 is lost, so the electromagnetic valve 974 creates a state of blocking the atmosphere between the pressure tank 971 and the recovery tank 92, and the application of the negative pressure P2 from the pressure tank 971 to the recovery tank 92 is blocked.

The pressure applying unit 97 has a check filter 975 between the pipe 944 and the solenoid valve 974. This check filter 975 allows the passage of gas from the recovery tank 92 to the pressure tank 971, while prohibiting the passage of ink from the recovery tank 92 to the pressure tank 971. In this way, the check filter 975 prevents ink from flowing from the recovery tank 92 into the tube 973.

The ink supply mechanism 9 further has a buffer tank 98 that communicates with the recovery tank 92 through a pipe 988. The buffer tank 98 communicates with the recovery tank 92 above the gas-liquid interface (i.e., the gas layer). In other words, gas moves between the buffer tank 98 and the recovery tank 92. On the other hand, ink does not move between the buffer tank 98 and the recovery tank 92, and no ink is present in the buffer tank 98. During both power transmission (Figure 3) and power outages (Figure 4), the buffer tank 98 and the recovery tank 92 are in communication with each other, and the pressure in the buffer tank 98 and the pressure in the recovery tank 92 are always equal.

3, the solenoid valve 974 creates an atmospheric communication state between the pressure tank 971 and the buffer tank 98 by the power supplied from the power supply circuit 94, and the negative pressure P2 inside the pressure tank 971 is applied to the inside of the buffer tank 98 via the tube 973, the solenoid valve 974, the piping 944, and the piping 988. On the other hand, during a power outage as shown in FIG. 4, the power supply from the power supply circuit 94 to the solenoid valve 974 is lost, so the solenoid valve 974 creates an atmospheric cut-off state between the pressure tank 971 and the buffer tank 98, and the application of the negative pressure P2 from the pressure tank 971 to the buffer tank 98 is cut off.

When power is being transmitted as shown in FIG. 3, the pressure P2 inside the recovery tank 92 and the buffer tank 98 is lower than the pressure P1 inside the supply tank 91, which causes ink to move from the supply tank 91 to the recovery tank 92 via the circulation path C. If this state continues, the liquid level in the supply tank 91 will drop and the liquid level in the recovery tank 92 will rise, and the meniscus required for the nozzle N of the ejection head H will no longer be generated. Therefore, the circulation pump 93 circulates the ink from the recovery tank 92 to the supply tank 91, thereby keeping the liquid levels in the supply tank 91 and the recovery tank 92 constant.

The ink supply mechanism 9 also includes an electromagnetic valve 99 provided in a pipe 999 that connects the atmosphere between the recovery tank 92 and the supply tank 91 in a manner that allows communication between them. In other words, an electromagnetic valve 99 is provided in parallel with the circulation pump 93 between the recovery tank 92 and the supply tank 91. This electromagnetic valve 99 is of a normally open type. Therefore, during power transmission as shown in FIG. 3, the electromagnetic valve 99 is opened by the power supplied from the power supply circuit 94, and the communication state of the atmosphere between the recovery tank 92 and the supply tank 91 via the electromagnetic valve 99 is cut off. On the other hand, during a power outage as shown in FIG. 4, the power supply from the power supply circuit 94 to the electromagnetic valve 99 is lost, so the electromagnetic valve 99 is closed, and the atmosphere between the recovery tank 92 and the supply tank 91 is communicated via the electromagnetic valve 99. As a result, the upper side of the gas-liquid interface in the recovery tank 92 (i.e., the gas layer) and the upper side of the gas-liquid interface in the supply tank 91 (i.e., the gas layer) are communicated.

Thus, when the solenoid valve 99 connects the recovery tank 92 and the supply tank 91 during a power outage (FIG. 4), the pressure in the recovery tank 92 and the pressure in the supply tank 91 become a predetermined negative pressure P3. This negative pressure P3 is higher than the negative pressure P2 and lower than the positive pressure P1. Incidentally, the negative pressure P2 is applied in advance to the buffer tank 98 during power transmission (FIG. 3), and the buffer tank 98 communicates with the recovery tank 92 and the supply tank 91 during a power outage (FIG. 4). Due to the function of the buffer tank 98, a certain degree of negative pressure P3 is maintained in the recovery tank 92 and the supply tank 91 during a power outage. On the other hand, as described above, each of the supply tank 91 and the recovery tank 92 is disposed above the discharge head H. Therefore, a head pressure corresponding to the difference in height is generated between the gas-liquid interfaces of the recovery tank 92 and the supply tank 91 and the nozzle N of the discharge head H. Therefore, the buffer tank 98 is provided with a volume large enough to generate a negative pressure P3 that maintains the ink against this head pressure.

The ink supply mechanism 9 according to the present embodiment described above circulates the ink through a circulation path C that passes from the recovery tank 92 to the supply tank 91 via the circulation pump 93, and then returns to the recovery tank 92 after passing from the recovery tank 92 to the ejection head H via the supply tank 91. In addition, an electromagnetic valve 99 is provided between the supply tank 91 and the recovery tank 92, and this electromagnetic valve 99 isolates the atmospheres between the supply tank 91 and the recovery tank 92 when power is applied (FIG. 3). Therefore, the electromagnetic valve 99 does not inhibit the generation of a pressure difference (=P2-P1) between the supply tank 91 and the recovery tank 92. On the other hand, this electromagnetic valve 99 communicates the atmospheres between the supply tank 91 and the recovery tank 92 when power is not applied (FIG. 4). Therefore, when the circulation pump 93 stops due to a power outage, the pressure difference between the supply tank 91 and the recovery tank 92 is quickly eliminated, and the ink can be prevented from flowing into the recovery tank 92 from the supply tank 91 via the ink supply chamber Hc of the ejection head H.

In particular, a buffer tank 98 (buffer section) is provided that communicates with the atmosphere of the recovery tank 92. When the atmospheres between the recovery tank 92 and the supply tank 91 are mutually isolated, a positive pressure P1 (first pressure) is applied to the supply tank 91, and a negative pressure P2 (second pressure) that is lower than the positive pressure P1 is applied to the recovery tank 92 and the buffer tank 98. In this configuration, when the atmospheres between the supply tank 91 and the recovery tank 92 are communicated, the difference between the positive pressure P1 in the supply tank 91 and the negative pressure P2 in the recovery tank 92 is eliminated, and the pressure in the recovery tank 92 rises. However, since the buffer tank 98 is provided separately from the recovery tank 92, the increase in pressure in the recovery tank 92 is suppressed compared to when the buffer tank 98 is not provided. Specifically, a negative pressure P3 (third pressure) that is higher than the negative pressure P2 and lower than the positive pressure P1 is generated in the recovery tank 92 and the supply tank 91, and this negative pressure P3 resists the head pressure between the recovery tank 92 and the supply tank 91 and the nozzle N of the ejection head H, preventing ink leakage from the nozzle N. In this way, it is possible to prevent ink leakage from the ejection head H when the pressure difference between the supply tank 91 that supplies ink to the ejection head H and the recovery tank 92 that recovers ink from the ejection head H is eliminated.

The pressure applying unit 96 (first pressure applying unit) has a solenoid valve 964 (first solenoid valve) and a pressure tank 961 (first pressure tank) that allows the atmosphere to communicate with the supply tank 91 via the solenoid valve 964, and applies the positive pressure P1 generated in the pressure tank 961 to the supply tank 91 via the solenoid valve 964. The solenoid valve 964 communicates the atmosphere between the supply tank 91 and the pressure tank 961 when energized, while blocking the atmosphere between the supply tank 91 and the pressure tank 961 when not energized. The pressure applying unit 97 (second pressure applying unit) has a solenoid valve 974 (second solenoid valve) and a pressure tank 971 (second pressure tank) that allows the atmosphere to communicate with the recovery tank 92 (and the buffer tank 98) via the solenoid valve 974, and applies the negative pressure P2 generated in the pressure tank 971 to the recovery tank 92 and the buffer tank 98 via the solenoid valve 974. The solenoid valve 974 communicates the atmosphere between the recovery tank 92 and the buffer tank 98 and the pressure tank 971 when energized, and blocks the atmosphere between the recovery tank 92 and the buffer tank 98 and the pressure tank 971 when deenergized. In this configuration, as the atmosphere between the supply tank 91 and the recovery tank 92 is communicated during a power outage, the pressure tank 961 and the pressure tank 971 are blocked from the atmosphere between the supply tank 91, the recovery tank 92, and the buffer tank 98. Therefore, the negative pressure P3 required to prevent ink leakage from the ejection head H can be reliably generated in each of the supply tank 91, the recovery tank 92, and the buffer tank 98.

In addition, during power transmission as shown in FIG. 3, a positive pressure P1 is applied to the supply tank 91. In this manner, in a configuration in which a positive pressure P1 is generated in the supply tank 91, the problem of ink leakage described above tends to become more pronounced. Therefore, a configuration in which a buffer tank 98 is provided as described above is particularly suitable.

In addition, applying positive pressure P1 to the supply tank 91 in the ink supply mechanism 9 for the ejection head H that ejects white ink has the following advantages. That is, white ink is often used to print so-called solid images that form backgrounds, etc. If the amount of white ink ejected from the ejection head H is insufficient when printing such a solid image, image defects such as streaks appearing in areas where the white ink does not adhere can occur. In response to this, applying positive pressure P1 inside the supply tank 91 allows a sufficient amount of white ink to be ejected from the ejection head H, making it possible to print a suitable solid image.

In the embodiment described above, the printing system 1 corresponds to an example of the "printing system" of the present invention, the printing device 3 corresponds to an example of the "printing device" of the present invention, the drying device 6 corresponds to an example of the "drying device" of the present invention, the supply tank 91 corresponds to an example of the "supply tank" of the present invention, the recovery tank 92 corresponds to an example of the "recovery tank" of the present invention, the circulation pump 93 corresponds to an example of the "circulation pump" of the present invention, the power supply circuit 94 corresponds to an example of the "power supply unit" of the present invention, the pressure application unit 96 corresponds to an example of the "first pressure application unit" of the present invention, the pressure tank 961 corresponds to an example of the "first pressure tank" of the present invention, and the solenoid valve 964 corresponds to an example of the "first electric the pressure applying unit 97 corresponds to an example of a "second pressure applying unit" of the present invention, the pressure tank 971 corresponds to an example of a "second pressure tank" of the present invention, the solenoid valve 974 corresponds to an example of a "second solenoid valve" of the present invention, the buffer tank 98 corresponds to an example of a "buffer unit" of the present invention, the solenoid valve 99 corresponds to an example of a "bypass solenoid valve" of the present invention, the ejection head H corresponds to an example of an "ejection head" of the present invention, the nozzle N corresponds to an example of a "nozzle" of the present invention, the positive pressure P1 corresponds to an example of a "first pressure" of the present invention, the negative pressure P2 corresponds to an example of a "second pressure" of the present invention, and the negative pressure P3 corresponds to an example of a "third pressure" of the present invention.

The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the pressure applied to the supply tank 91 from the pressure tank 961 of the pressure application unit 96 does not need to be positive pressure, and may be negative pressure. In particular, in the ink supply mechanism 9 that supplies ink to the ejection head H that ejects color ink, a negative pressure (first pressure) higher than the negative pressure P2 may be applied to the supply tank 91 during power transmission.

In addition, a redundant pipe may be provided instead of the buffer tank 98 described above as a "buffer section" to which negative pressure P2 is applied in advance during power transmission.

Furthermore, the above-mentioned solenoid valves 974, 964, and 99 do not need to be configured as single valves, but may be configured together as a multi-way valve.

The present invention is applicable to all printing technologies.

REFERENCE SIGNS LIST 1... Printing system 3... Printing device 6... Drying device 91... Supply tank 92... Recovery tank 93... Circulation pump 94... Power supply circuit (power supply unit)
96: Pressure applying portion (first pressure applying portion)
961...Pressure tank (first pressure tank)
964...Solenoid valve (first solenoid valve)
97: Pressure applying portion (second pressure applying portion)
971...Pressure tank (second pressure tank)
974...Solenoid valve (second solenoid valve)
98...Buffer tank (buffer section)
99...Solenoid valve (bypass solenoid valve)
H: Discharge head N: Nozzle P1: Positive pressure (first pressure)
P2: negative pressure (second pressure)
P3: Negative pressure (third pressure)

Claims (6)

an ejection head that ejects ink from a nozzle;
a recovery tank that stores ink recovered from the ejection head;
A buffer section communicating with the recovery tank;
a supply tank that stores ink to be supplied to the ejection head;
a first pressure applying unit that applies a first pressure to the inside of the supply tank;
a second pressure applying unit that applies a second pressure, which is a negative pressure lower than the first pressure, to the inside of the recovery tank and the inside of the buffer unit;
a circulation pump that uses the supplied power to perform a liquid transfer operation for transferring ink from the collection tank to the supply tank;
a bypass solenoid valve provided between the supply tank and the recovery tank, for isolating the supply tank and the recovery tank from each other when energized, and for connecting the supply tank and the recovery tank to each other when deenergized;
a power supply unit for supplying power to the circulation pump and the bypass solenoid valve,
The recovery tank is disposed above the ejection head,
A printing device in which the buffer unit is connected to the recovery tank and the supply tank when the bypass solenoid valve is not energized, and generates a third pressure in the recovery tank and the supply tank, which is a negative pressure higher than the second pressure and lower than the first pressure, and the third pressure resists the head pressure between the recovery tank and the supply tank and the nozzle of the ejection head to prevent ink leakage from the nozzle. the first pressure applying unit has a first solenoid valve and a first pressure tank connected to the supply tank via the first solenoid valve, and applies the first pressure generated in the first pressure tank to the supply tank via the first solenoid valve;
the first solenoid valve, when energized, connects the supply tank and the first pressure tank, and, when deenergized, isolates the supply tank and the first pressure tank from each other;
the second pressure applying unit has a second electromagnetic valve and a second pressure tank connected to the recovery tank via the second electromagnetic valve, and applies the second pressure generated in the second pressure tank to the recovery tank via the second electromagnetic valve;
The printing apparatus according to claim 1 , wherein the second solenoid valve connects the collection tank and the second pressure tank when energized, and isolates the collection tank and the second pressure tank from each other when deenergized. The printing device according to claim 1 or 2, wherein the first pressure is a positive pressure. The printing device according to claim 3, wherein the ink is white ink. A printing device according to any one of claims 1 to 4,
a drying device that dries the ink ejected onto a print medium by the printing device. a step of applying a first pressure to a supply tank connected to a discharge head that discharges ink from nozzles to perform printing, while applying a second pressure, which is a negative pressure lower than the first pressure, to a recovery tank connected to the discharge head and to a buffer section communicating with the recovery tank, thereby supplying ink from the supply tank to the discharge head and recovering ink from the discharge head to the recovery tank;
supplying power to a circulation pump disposed between the recovery tank and the supply tank to send ink from the recovery tank to the supply tank;
a printing method comprising a step of, when the supply of power to the circulation pump is stopped, connecting the recovery tank and the supply tank to each other, and connecting the buffer unit to the recovery tank and the supply tank to generate a third pressure in the recovery tank and the supply tank, the third pressure being a negative pressure higher than the second pressure and lower than the first pressure, and preventing ink leakage from the nozzles by resisting a head pressure between the recovery tank and the supply tank and the nozzles of the ejection head.

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